An in-cylinder injection type internal combustion engine that directly injects fuel into a combustion chamber is widely known. The in-cylinder injection type internal combustion engine performs direct fuel injection into the combustion chamber with a fuel injection valve, and achieves a reduction in exhaust gas substance and fuel consumption, enhancement in output, and the like.
In the in-cylinder injection type internal combustion engine, the injected fuel may attach to a piston crown surface or a cylinder bore wall surface depending on a fuel injection timing.
If an amount of fuel attaching to/remaining on the cylinder bore wall surface is large, such fuel may not be completely vaporized until ignition in some cases, so that unburned gas is apt to increase. Therefore, for example, JP 2009-102997 A and JP 2009-102998 A disclose a technology of changing, when a temperature on the cylinder bore wall surface is low, the fuel injection timing from an injector in an intake stroke so that the fuel can spread over the piston crown surface and easily vaporized.
In addition, JP 2002-161790 A discloses a technology in which fuel injection is performed a plurality of times in one burning cycle, and the fuel injection amount for each time is accordingly made small, to thereby reduce the fuel attachment to the cylinder bore wall surface, and an interval between one injection and the next injection is kept constant at a rough crank angle with respect to a change in operation conditions of an engine, that is, the injection interval is set to be longer as the rotation becomes lower and is set to be shorter as the rotation becomes higher, to thereby spray the fuel in a dispersed manner.
Meanwhile, if an amount of fuel attaching to and remaining on the piston crown surface and the cylinder bore wall surface is large, the number of exhaust particles of particulate substances (hereinafter, referred to as PM) is apt to increase. In particular, if the amount of fuel attaching to the piston crown surface is large, the number of exhaust particles of PM is apt to increase. In recent years, because of air pollution and impact on human health, there is an increasing need for the in-cylinder injection type internal combustion engine to reduce the number of exhaust particles of PM.